Conventionally, in a battery-driven electronic apparatus, a user is informed of a battery residual capacity (electric power) by battery indication so that the user can easily determine time to electrically charge the battery.
As methods for battery residual capacity detection, a current integration method using a specialized IC to integrate charging/discharging battery current and calculate a residual capacity, a voltage detection method of estimating a residual capacity based on the result of detection of battery voltage utilizing the characteristic of discharging voltage which is gradually reduced accompanying the reduction of residual capacity and the like are known. For example, the former method is adopted in notebook type PCs and cam coders, while the latter method is adopted in digital cameras and cellular phones. The latter voltage detection method is disadvantageous in detection accuracy in comparison with the former current integration method, however, in the latter method, as the number of parts is smaller, the latter method is advantageous in cost and size. According to the voltage detection method, an output voltage from a battery is converted by an analog-digital converter to a digital signal, and the digital value is compared with a predetermined threshold value, thereby the residual capacity of the battery is determined. The result of determination is displayed on a battery indicator such as a liquid crystal display or LED for a user.
For example, in the case of notebook type PC including, as its driving power source, an AC adapter and a battery, as standard equipments, a battery charging circuit and a battery indicator are generally included in the notebook type PC main body. However, in the case of small image printing apparatus such as an ink jet printer, generally, only an AC adapter is included as a standard equipment but a battery, which is a second driving power source, is an optional equipment. In a case where a battery charging circuit and a battery indicator, which are necessary only upon use of the optional battery, are installed in the printing apparatus main body as in the case of the notebook type PC, unnecessary cost increase and upsizing are imposed on a user who does not require a battery. Accordingly, in some cases, the battery charging circuit is provided as a separate unit from the printing apparatus main body, and is handled as an optional equipment similar to the battery.
However, even in this case, as the battery indicator is provided in the printing apparatus main body, the unnecessary cost increase and upsizing are still imposed on a user who does not require a battery. Such load on the user is caused mainly by adoption of battery residual capacity detection based on the voltage detection method which can be realized at the lowest cost without size increase. The adoption of the voltage detection method has the merit as described above, and has almost no demerit of cost increase and upsizing even though the battery residual capacity detection method is implemented in the apparatus main body. However, this method has a technical limitation that if driving load on the apparatus upon battery voltage detection is not constant, a proper battery residual capacity cannot be detected.
Since the driving load on the printing apparatus is not always constant, it is necessary to detect the battery voltage when the driving load is constant so as to determine the battery residual capacity. However, as the timing of detection cannot be found from the outside of the printing apparatus main body, the battery residual-capacity detection function is provided in the printing apparatus main body, and the battery indicator is also provided in the apparatus main body. As for a printing apparatus driven by a battery or commercial power supply, in order to suppress the cost increase and upsizing of the printing apparatus main body due to the existence of the battery indicator included in a battery pack, it may be arranged such that a battery residual-capacity management module based on the current integration method comprising a microcomputer specialized for battery residual capacity management is provided in the battery pack. However, this imposes serial cost increase and upsizing of the battery pack on a user who does not require a battery.